A radiation-collecting device is typically a photovoltaic module comprising at least one photovoltaic cell suitable for collecting and converting the energy from radiation into electrical energy. A radiation-emitting device is typically an OLED device comprising at least one organic light-emitting diode, or OLED, suitable for converting electrical energy into radiation.
In a known manner, the energy conversion elements of a device that collects or emits radiation, namely the photovoltaic cells in the case of a photovoltaic module or the OLED structures in the case of an OLED device, comprise a material suitable for providing the energy conversion and two electrically conductive contacts on both sides of this material. However, regardless of their manufacturing technology, such energy conversion elements are susceptible to degradation under the effect of environmental conditions, in particular under the effect of exposure to air or to moisture. By way of example, for OLED structures or organic photovoltaic cells, the front electrode and the organic material are particularly sensitive to environmental conditions. For thin-film photovoltaic cells comprising an inorganic absorber layer, the front electrode of the cell, formed based on a transparent conductive oxide (or TCO) layer or based on a transparent conductive coating (or TCC), is also very sensitive to environmental conditions.
In order to protect the energy conversion elements of a device that collects or emits radiation with respect to degradations due to exposure to air or to moisture, it is known to manufacture the device with a laminated structure, in which the energy conversion elements are encapsulated and combined at least with one transparent front substrate. This front substrate is placed on the side on which radiation is incident on the device in the case of a photovoltaic module, or on the side on which radiation is extracted from the device in the case of an OLED device.
Depending on the application of the device, it may be desirable to combine the energy conversion elements with a light flexible substrate, rather than a glass substrate. Such a light flexible substrate is typically a substrate composed of a transparent thermoplastic polymer, for example made of polyethylene, polyester, polyamide, polyimide, polycarbonate, polyurethane, polymethyl methacrylate or a fluoropolymer. It has however been observed that when a radiation-collecting or radiation-emitting device comprises a polymer front substrate, the device exhibits a high degree of degradation. This is because a polymer substrate, which has a high permeability, is not able to prevent the migration of contaminants such as water vapor or oxygen to the energy conversion elements.
US-A-2004229394 describes a protective front substrate for a photovoltaic module that comprises a polymer film and a barrier layer deposited on the face of the polymer film intended to be facing the inside of the module. This barrier layer makes it possible to limit the migration of gases from the polymer film to the photovoltaic cell. However, due to the presence of this barrier layer, the transmission of radiation to the photovoltaic cell is capable of being degraded, hence there is a risk of reducing the photovoltaic efficiency of the photovoltaic module.
It is these drawbacks that the invention intends more particularly to remedy by proposing a protective substrate which, when it is integrated into a device that collects or emits radiation, gives this device improved resistance, especially to air and to moisture, by providing an effective and very long-term protection of the energy conversion elements of the device that are sensitive to air and/or moisture, while preserving the energy conversion efficiency of the device, or even increasing this efficiency.